Currently, display devices have different electro-optical characteristics of red, green and blue colors on the display screen, resulting in a large difference in the color of each grayscale. Only when the colors of the grayscales are the same, the color temperature can be adjusted to the desired color temperature by the white balance adjustment of the bright and dark fields. Therefore, it is necessary to correct the color of each grayscale to clear the color error of each grayscale, so that the display can be adjusted by white balance. Clearing the color error of each grayscale can be achieved by gamma correction of the display.